The very high bandwidth of optical fibres has caused a great increase in data transmission speeds within networks over the past decade. In many systems the optical signals are converted into electrical signals at connection nodes. The routing of the data around the network is then performed in the electrical domain by analysing the electronic signals. This places a limit on the speeds that can be obtained, since electrical signal processing and operation of electrical switches is inherently slow relative to all optical processing.
Various optical routers are known, perhaps the most widely used being optical amplifiers which can be placed at nodes in a network to increase the transmission length of the network. These devices boost the level of the signal, allowing long distances to be traversed despite transmission losses. However, such devices do not switch the path of the signals around the network.
Several attempts have been made to provide all optical switches but to date the applicant is not aware of any devices which can be successfully integrated into an optical transmission network. Devices which use interferometric principles have been proposed which can perform two by two switching, but they are as yet not widely established.
The function of a two by two (2×2) switch assembly is to divert incoming data streams onto one of two output paths. The switch typically operates between two configurations: a bar state and a cross-over configuration. In the bar configuration the first input stream is passed to a first output path, and the second input stream to a second output path. In the cross-over configuration the first input stream is passed to the second output path and the second input stream to the first path. The state of the switch is determined by reading the routing information contained within the incoming data packets, typically by electronic processing of the signals.